Skin diseases represent major health care challenges today. For example, over five million Americans and over one hundred million people worldwide suffer from psoriasis. Detection, diagnosis, and staging of a skin disease is an important aspect of its management. Current diagnostic methods rely mainly on visible observation and biopsies. However, detection methods for skin diseases that rely on visible observation are not effective for diagnosing many skin diseases, and do not detect diseases until after clinical manifestation. Invasive methods such as biopsies, not only are traumatic for a subject being tested, they also increase the risk of infection. Furthermore, invasive methods do not provide an enriched sample of cells on the surface of skin, which are the cells involved in a surface reaction.
Detection and diagnosis of skin disease are important not only for patient management, but also to assess the safety and efficacy of new skin disease therapeutic agents and new skin care products. New therapeutic agents are required for many skin diseases where present therapeutic agents are not fully effective. Furthermore, diagnostic methods provide important information regarding the specific genetic changes underlying a subject's skin disease. Identifying these genetic changes identifies potential drug targets and may be critical in determining whether a person will respond to a particular therapeutic agent.
In addition to assessing new therapeutic agents, detection and diagnosis methods are also important to assess the safety of new skin care products. Skin care products, including cosmetics, are an important part of most people's daily grooming habits. The average adult uses at least seven different skin care products each day. Currently, all commercial skin care products are required to undergo safety testing. These tests take the form of Clinical Acute Primary Irritation and 14-day Cumulative Irritation Protocols followed by Human Repeat Insult Patch Testing (HRIPT) to detect sensitization (contact allergy). Visual analysis is used to determine the test results as described in Richard Berger and James Bowman, A reappraisal of the 21-day cumulative irritancy test in man, J. Toxicol-Cut and Ocular Toxicol 1(2), 101–107 (1982). Therefore, allergic reactions are not detected until they have manifested themselves in a visible reaction.
In addition to issues related to relatively late stages of detection, visible analysis cannot distinguish subtle skin reactions that are difficult to classify as irritant or allergic reactions. This classification distinction is very important because it can be used as the basis for deciding whether to continue to develop a new skin care product. Issues of irritation can be dealt with by reformulation, whereas issues of sensitization (i.e. an allergic reaction) can require more drastic product altering actions due to safety and liability concerns. Therefore, misdiagnosis of irritant dermatitis as allergic dermatitis can block a safe and efficacious skin care product from being available to people who could benefit from it.